Question: If $3a + 9b + 7c = 5$ and $8x + 5y + 8z = 1$, what is $-21c - 8x - 27b - 9a - 8z - 5y$ ?
$= -9a - 27b - 21c - 8x - 5y - 8z$ $= (-3) \cdot (3a + 9b + 7c) + (-1) \cdot (8x + 5y + 8z)$ $= (-3) \cdot (5) + (-1) \cdot (1)$ $= -15 - 1$ $= -16$